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Scientists plan to use “clocks” from dead stars to illuminate the most mysterious thing in the universe: dark energy.
These timekeepers are actually pulsarsor rotating quickly neutron stars It is born when stars with at least eight times the mass of the Sun die. The extreme conditions of neutron stars make them ideal laboratories for studying physics in environments found nowhere else in the universe.
So called “millisecond pulsars“can spin hundreds of times per second and emit beams of electromagnetic radiation from their poles, like cosmic beacons, that sweep across space. They get their name because, when they were initially spotted, these neutron stars appeared to be pulsating, increasing in brightness as they its beams were aimed directly at Earth.
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The ultra-precise timing of pulsars’ brightness variation to the millisecond means they can be used collectively as cosmic clocks in “pulsar timing matrices.” These arrays are so precise that they can measure gravitational perturbations in the structure of space and time, united as a four-dimensional entity called “spacetime,” which could be the ideal way to hunt for dark matter.
“Science has developed very precise methods for measuring time,” said researcher John LoSecco of the University of Notre Dame in a statement. “On Earth we have atomic clocks and in space we have pulsars.”
Closing the mystery of dark matter
Dark matter is so mysterious because it doesn’t interact with light or ordinary matter – or, if it does, it does so very weakly and we can’t detect it. “Ordinary matter” is made up of atoms made up of electrons, protons and neutrons that interact with light and matter, so scientists know that dark matter must be made up of other particles.
Despite not interacting with light, dark matter has a gravitational influence, and its presence can be inferred when this influence affects light and, in fact, ordinary matter. It is the effect of this gravitational influence on light that LoSecco and colleagues set out to explore using pulsars.
According to Albert Einstein’s theory of general relativity, objects with mass curve the very structure of space-time, and gravity arises from this curvature. When light passes through this curvature, its path is also diverted. This can change the travel time of light, causing light from the same distant body to arrive at Earth at different times, in theory “slowing” it (the speed of light isn’t actually changed; it’s the distance it travels). that changes). ).
Dark matter has mass, and therefore concentrations of this mysterious form of matter can also distort space-time. Thus, the path of light from distant objects is curved and its arrival time is delayed when it passes through concentrations of dark matter. This effect is called “gravitational lens”, with the intervening body changing the path of light called “gravitational lensing”.
LoSecco and colleagues examined data collected from 65 pulsars in the Parkes pulsar timing matrix. They observed about 12 incidents that indicated variations and delays in the pulsars’ timings, which are generally accurate to the nanosecond.
This indicates that beams of radio waves from these cosmic beacons of dead stars are traveling around a warp in space caused by a concentration of invisible mass somewhere between the pulsar and the telescope. The team theorizes that these invisible masses are candidates for dark matter “clusters.”
“We take advantage of the fact that the Earth is moving, the Sun is moving, the pulsar is moving, and even dark matter is moving,” LoSecco said. “We observe deviations in arrival time caused by the change in distance between the mass we are observing and the line of sight of our ‘clockwise’ pulsar.”
The deviations observed by the team are absolutely minimal. To illustrate this, a body with the mass of the sun would cause a delay in the pulsar’s radio waves of about 10 microseconds. The proposed deviations in dark matter delay seen by the team are 10,000 times smaller than this.
“One of the findings suggests a distortion of about 20% of the Sun’s mass,” said Professor LoSecco. “This object could be a candidate for dark matter.”
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A side effect of the team’s research is the improved accuracy of Parkes Pulsar Timing Array data, which is collected to look for evidence of low-frequency gravitational radiation.
Dark matter clusters can add interference or “noise” to this data; Identifying and removing this noise will help scientists better use this set of samples in the search for low-frequency ripples in spacetime, called gravitational waves. This could allow the detection of gravitational radiation from more distant and therefore earlier black hole mergers – and perhaps even from background primordial gravitational waves left over from the big Bang.
“The true nature of dark matter is a mystery,” said LoSecco. “This research sheds new light on the nature of dark matter and its distribution in the Milky Way and may also improve the accuracy of precise pulsar data.”
The team’s results were presented in the National Astronomy Meeting (NAM) 2024 Reunion at the University of Hull on Monday (15 July).
